have you read SCP-209? concept-wise, this is too similar, which means you need something to make it different, as in narratives, stories. 209 has better mechanics too—how convenient is it for the poet to be "Controllers" and doesn't suffocate himself to death, eh?

barring that, Euclid designation seems fine, but the containment procedure is a load of nonsense. Why would we need a 3x3x3 meter room and 4 guards for mere stone tablet? Heck, why do we preserve the tablet at all? The anomaly is the sound of the phrase, right? Record it on an audio file, encrypt it with 2048-bit key and lock it in standard locker or something.